Nowhere in the Bill of Rights is the influence of James Madison stamped more unmistakably than in the first part of the 1st Amendment pertaining to the Freedom of Religion.
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.
Note that there are two religion clauses. The first, called the “Establishment Clause,” prohibits government from declaring an official religion. The second, called the “Free Exercise Clause,” guarantees the freedom to worship as one chooses. These two important concepts are related, but distinct. Sometimes, they can even conflict with one another. Debates about precisely what they mean have been going on for hundreds of years and continue to this day.